Several medical applications use ultrasonic energy. For example, U.S. Pat. Nos. 4,821,740, 4,953,565 and 5,007,438 disclose the use of ultrasonic energy to enhance the effect of various therapeutic compounds. An ultrasonic catheter can be used to deliver ultrasonic energy and a therapeutic compound to a treatment site within a patient's body. Such an ultrasonic catheter typically includes an ultrasound assembly configured to generate ultrasonic energy and a fluid delivery lumen for delivering the therapeutic compound to the treatment site.
As taught in U.S. Pat. No. 6,001,069, ultrasonic catheters can be used to treat human blood vessels that have become partially or completely occluded by plaque, thrombi, emboli or other substances that reduce the blood carrying capacity of the vessel. To remove or reduce the occlusion, the ultrasonic catheter is used to deliver solutions containing therapeutic compounds directly to the occlusion site. Ultrasonic energy generated by the ultrasound assembly enhances the effect of the therapeutic compounds. Such a device can be used in the treatment of diseases such as ischemic stroke, peripheral arterial occlusion or deep vein thrombosis. In such applications, the ultrasonic energy enhances treatment of the occlusion with therapeutic compounds such as urokinase, tissue plasminogen activator (“tPA”), recombinant tissue plasminogen activator (“rtPA”) and the like. Further information on enhancing the effect of a therapeutic compound using ultrasonic energy is provided in U.S. Pat. Nos. 5,318,014, 5,362,309, 5,474,531, 5,628,728, 6,001,069 and 6,210,356.